The present invention relates generally to radio energy transmission, and more specifically related to a distributed antenna for transporting radio energy through a defined medium.
The performance of indoor wireless communication systems, such as a radio frequency identification (RFID) system or wireless local area networks (WLANs), depends on the signal strength available at the receiving antenna, or more specifically, the signal-to-noise ratio (SNR) that the systems can obtain at the receiving end. Most systems use a single base station antenna that broadcasts enough power to sufficiently cover a given area. However, the signal strength may have a very significant variation, which is determined by the distance from the base station antenna to the receiver, signal attenuation caused by intervening structures between the base station and the receiver and the multi-path caused by scattering from nearby structures. Hence, the coverage is always limited, and an improvement is implemented to use higher transmitting power and/or multiple base stations to provide proper coverage for larger areas.
An example of a problematic indoor wireless environment is a room or enclosure that is long and narrow, such as a hallway, a long warehouse or factory, an aircraft cabin or a passenger car on a train. A single base station antenna in such an environment will not provide uniform coverage because the signal will be attenuated along the length of the enclosure. Therefore, multiple base stations or multiple antennas would need to be deployed in a distributed fashion in such a way that the coverage is uniform along the whole enclosure. Such a system would be complex, expensive, and invasive using existing technologies.
Another example of a communication system is the RFID system using RF transmission to identify, categorize, locate and track objects. The system is made up of two primary components: a transponder or the RFID tag and a reader. The tag is a device that generates electrical signals or pulses interpreted by the reader. The reader is a transmitter/receiver combination (transceiver) that activates and reads the identification signals from the transponder.
RFID tags are considered to be intelligent bar codes that can communicate with a networked system to track every object associated with a designated tag. RFID tags will communicate with an electronic reader that will detect the “tagged” object and further connects to a large network that will send information on the objects to interested parties such as retailers and product manufacturers. For example, the tag can be programmed to broadcast a specific stream of data denoting identity such as serial and model numbers, price, inventory code and date. Therefore, the RFID tags are expected to be widely used in the wholesale, distribution and retail businesses.
A reader also contains an RF antenna, transceiver and a micro-processor. The transceiver sends activation signals to and receives identification data from the tag. The antenna may be enclosed within the reader or located outside the reader as a separate piece. The reader may be either a hand-held or a stationary component that checks and decodes the data it receives.
It is of interest to communicate with RFID tags attached to merchandise (or containers) stored on shelves in a warehouse or retail establishment. With existing technology, this may be achieved in one of two ways: (1) a mobile RFID scanner that moves along the shelves, possibly hand-held, or (2) by mounting a large number of fixed scanners to cover all the shelves. The former approach is very time consuming and labor-intensive, while the latter approach is very complex and expensive. Furthermore, in the case of having multiple fixed scanners or base station antennas, it is difficult to conceal these devices in an aesthetically pleasing manner.
In view of the above applications, there is clearly a need to develop a system of improved wireless coverage without greatly increasing the level of complexity and cost for a wireless system such as the RFID system.